1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and devices for stabilizing a tailbuoy attached to a streamer towed during a marine survey; more particularly, some embodiments are directed to or include a tailbuoy with a keel configured to decrease the tailbuoy's lateral deviations.
2. Discussion of the Background
Interest in developing new oil and gas production fields has dramatically increased in recent years. However, the availability of land-based production fields is limited, so the industry has extended drilling offshore to locations likely to hold a vast amount of fossil fuel. Marine surveys, which generate a profile (image) of the geophysical structure under the seafloor, are used to identify these locations.
During a marine survey, as shown in FIG. 1, a vessel 10 tows a seismic source (not shown) and plural streamers 20 carrying seismic detectors 22 (only one detector is labeled). The streamers 20 are deployed in a predetermined configuration (e.g., parallel to the towing direction T) and are connected to vessel 10 via lead-in cables 14. Deflectors 16 and ropes 18 are used to deploy and maintain the streamers' 20 forward ends at predetermined lateral distances there-between.
Streamers 20 may be thousands of meters long (e.g., 10 km) and are usually towed at a depth of 10 m or more. Various causes (e.g., currents, local variation) may make portions of the streamers 20 deviate from the intended configuration (e.g., deviate from towing direction T). To alleviate these deviations, one or more devices named “birds” 24 (only one bird is labeled in FIG. 1, but plural birds are illustrated) may be attached to the streamers 20. Birds are configured to maintain/adjust the depth and/or lateral position of the streamers 20. Tailbuoys 30 are attached to streamers 20 to signal the streamers' distal end positions at the water surface.
It has been observed that tailbuoys 30 are very unstable, showing frequent and abrupt lateral deviations relative to towing direction due to local effects (e.g., surface waves and currents). Further, because modern streamers may be towed deeper or have a curved profile, a streamer's distal end may reach a depth of about 30 m or more. Due to these greater depths, it becomes necessary to use longer cables to connect the streamer's distal end to the tailbuoys, which cables make larger angles with the water's surface while the streamer and tailbuoy are towed. Such changes related to the cables used to tow tailbuoys create even greater tailbuoy instability. Accordingly, it would be desirable provide a mechanism that stabilizes a tailbuoy's motion and decreases lateral deviations.